Permanent-magnet uniform-field-producing apparatus



Jan. 4, 1966 R. ADLER 3,227,931

PERMANENT-MAGNET UNiFORM-FIELD-PRODUCING APPARATUS I Filed July 18, 1963 EQUI- POTENTIAL PLANES H .ZZ/

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| i N "Hi ll HH'H' INVENT R. Roberf 161 Q2 q t glgi'iilu 1 1 s 36 BY a) mi 37 United States Patent Ofiice 3,227,931 Patented Jan. 4, 1966 3,227,931 PERMANENT-MAGNET UNlFORM-FlELD- PRODUCING APPARATUS Robert Adler, Northfield, Ill., assignor to Zenith Radio Corporation, Chicago, 111., a corporation of Delaware Filed July 18, 1963, Ser. No. 296,068 20 Claims. (Cl. 317200) This invention pertains to magnetic elements. It is applicable, for example, to a magnet assembly which may be utilized in place of a solenoid for producing a magnetic field necessary to the proper operation of devices such as electron beam parametric amplifiers, traveling wave tubes, transducers, and the like.

To achieve proper operation of various electron beam tubes, it often is necessary to produce a homogeneous magnetic field having its flux lines parallel to the tube axis. The space which must be filled with magnetic flux has the shape of a long cylinder of relatively small diameter. In a typical present-day electron beam parametric amplifier tube, the cylindrical space is about six inches long and two inches in diameter. A conventional lownoise traveling wave tube may need a uniform field of the order of twelve inches long and with a diameter of about one inch.

Uniform magnetic fields of such shape, with the flux lines parallel to the axis of the cylindrical space, are conventionally produced by shielded solenoids. However, such solenoids require regulated DC. power, and for fields having a strength exceeding approximately 500 gauss, cooling is usually necessary. The power and cooling requirements often result in prohibitive increases in Weight and size.

It has heretofore been difiicult to produce a uniform field of the kind described by means of a permanent magnet. The usual permanent magnet assembly wastes most of the magnet volume. The conventional approach is to surround the cylindrical space with magnetic material shaped to form a sleeve which is magnetized longitudinally. The inefficiency of such permanent magnets arises because of a fundamental difference between the magnetized sleeve and the solenoid. In the case of the solenoid, the flux directions inside and outside solenoid are opposite; the flux lines external to the solenoid constitute the return path of the internal flux lines. Often, a high permeability shield surrounds the solenoid so that the reluctance of the external fiux path is reduced to near zero; consequently, the space internal of the solenoid is the only region to be supplied with magnetic energy. In comparison, the magnetized sleeve described above produces flux of the same polarity, or flux lines of the same direction, both inside and outside the sleeve; the return path for all flux is through the walls of the sleeve itself. With this approach, the entire flux outside the sleeve constitutes objectionable leakage, and in practice the useful re- .gion inside the sleeve receives only a very minor fraction of the total magnetic energy.

The efficiency of the permanent magnet sleeve decreases with an increase in the ratio of length to diameter. To accommodate the increase in the amount of stray flux, the walls of the sleeve usually are made thicker, particularly near its center. Permanent magnets which have been built to produce a uniform magnetic field of a strength up to only a few hundred gauss, such as employed for traveling Wave tubes, take the form of heavy, egg-shaped castings having a tunnel along the axis. Usually, the stray field extends much further than permissible, as a result of which the casting must be enclosed within a box of shielding material; however, the presence of this shield further increases the leakage flux and distorts the field pattern. In practice, such magnets are often entirely impracticable because of their large weight and the excessive amount of the stray field.

Many other devices require for their ope-ration unidirectional magnetic fields with a cross section that is small compared to the length of the flux path. Various transducers, for example, employ a DC. solenoid to develop such a field. While permanent magnets also have been employed, they lack efiiciency, and for reasons stated above it is difficult to shield properly the stray flux paths of such magnets without further reducing the efiiciency of the magnet.

Accordingly, it is a general object of the present invention to provide magnetic elements and permanent magnetic assemblies which avoid the afore-noted difficulties and deficiencies.

It is another object of the present invention to provide a magnet assembly which is an analog of a solenoid.

It is a particular object of the present invention to provide an improved flux producing assembly which requires no external power source or cooling means and which may be entirely shielded so that it produces no external stray fields.

It is also an object of the present invention to provide a flux-producing assembly capable of developing high field strengths while yet being of comparatively small size and weight.

In accordance with the invention, a magnetic assembly includes a magnet which is magnetized to define a plurality of equi-potential planes generally flat, parallel, uniformly spaced and perpendicular to an axis along which the magnet is disposed. Associated with the magnet is a body of magnetic material disposed along the axis and effectively having a common boundary with sidewalls of the magnet. The body defines a space on the axis and has magnetostatic equi-potential planes establishing a gradient along the common boundary which corresponds to that defined by the equi-potential planes in the magnet and which define in the space a plurality of flat, parallel equi-potential planes uniformly spaced along and perpendicular to the axis.

A feature of the invention is a magnetic insulator which comprises a body of effectively unity permeability material which exhibits substantially zero flux density and is magnetized to produce a magnetostatic potential which increases generally linearly along one boundary of the body. According to a particular aspect of the invention, the body has a cross-section of generally triangular shape and is magnetized in a direction perpendicular to one side of the triangle to produce a magnetostatic potential which increases generally linearly along one other boundary thereof.

In accordance with another aspect of the present invention, a magnetic assembly includes a magnet which is polarized to develop within its interior flux lines disposed generally parallel to a predetermined axis. The assembly further includes flux-opposing means defining a space on the axis adjacent one surface of the magnet and having a permanent magnet material disposed in series with the normal stray flux path from the space to the oppositely polarized surface of the magnet. The flux-opposing means has a magnetization potential and polarity of magnitude and direction to establish minimum flux density in the stray fiux path. The assembly defines a return flux path around the flux-opposing means from the end of the space remote from the one magnet surface to its other surface.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numbers identify like elements, and in which:

FIGURE 1 is a perspective view, partially broken away, of a shielded permanent magnet assembly constructed in accordance with the present invention;

FIGURE 2 is a diagrammatic longitudinal cross-sec tional view of the assembly of FIGURE 1;

FIGURE 3 is a graph illustrating a portion of the hysteresis curve of a material utilized in the assembly shown in FIGURES 1 and 2;

FIGURE 4 is a longitudinal cross-sectional view of an alternative embodiment of the present invention;

FIGURE 5 is a side elevational view of another alternative form of the present invention; and

FIGURE 6 is a graph illustrating a portion of the hysteresis curve of a material utilized in the assembly shown in FIGURE 5.

As described and depicted herein in order to illustrate the present invention, the assemblage takes a form suitable to serve in place of the conventional solenoid employed with an electron beam device to develop a uniform, homogeneous magnetic field which is traversed by the beam in a direction generally parallel to the lines of flux. Viewed externally, assembly 10 has the shape of two cone frustums of unequal height and with a common base. Forming an envelope of the assembly is a magnetic shield 11. Centered on the axis 12 of the assembly is a cylindrical magnet 13 from the internal end of which toward the opposite end of assembly 1% is defined a space or drift region 14. Surrounding magnet 13 is a mantle or body 15 of magnetic material. Body 15 has an exterior surface conforming to the internal surface of shield 11 and internally defines a hollow cylinder in which magnet 13 is received and the walls of which beyond the magnet define the lateral boundaries of space 14.

Magnet 13 is polarized to develop flux lines aligned parallel to axis 12 and having a uniform spacing lateral thereto so as to produce a homogenous field. The magnetostatic potential within the magnet has a gradient establishing equi-potential planes 21 perpendicular to axis 12 and which are flat, uniformly spaced and parallel. The potential gradient established by equi-potential planes 21 increases linearly from zero at the outer end surface 22 of the magnet to a maximum at its inner end surface 23.

Mantle 15 is a magnetic insulator which exhibits substantially zero flux density. To this end, it is composed of a material of effectively substantially unity permeability and which is magnetized to produce a magnetostatic potential that changes linearly along its internal boundary 24. One portion of boundary 24 lies adjacent the lateral surface of magnet 13 and the other defines the sidewall of space 14.

The operating characteristics of mantle 15 are illustrated in FIGURE 3 which depicts the significant portion of the hysteresis loop of the material. apparatus, such a material usually is operated at a point P which corresponds to the maximum product of the flux density B and the coercive force H. In this instance, however, the material is made to operate at point P which corresponds to maximum coercive force and zero flux density. Consequently, many conventional magnetic materials that are designed to produce high BH products are not necessarily the best materials to be chosen for this application. Instead, it is desirable to utilize a material having a very high coercive force H but a correspondingly low ability to carry flux. With these characteristics, the material affords a wide tolerance to deviations in the chraacter of magnetization. However, the slope of the BH characteristic cannot be smaller than unity, which corresponds to material the polarization of which remains constant. Satisfactory materials are the barium ferrite ceramics.

As illustrated, mantle 15 is composed of two annular frusto-conical sections 26 and 27 having a common base along the plane indicated by dashed line 28. Conse- In conventional lquently, sections 26 and 27 each have a triangular longitudinal cross-sectional area, longitudinal referring to the general direction of axis 12 which lies in the plane of the cross-section. Each of the sections is magnetized in a di rection perpendicular to the outer side of the triangle to produce a potential variation along boundary 24 which increases from the end of assembly 10 near magnet surface 22 linearly to plane 28 at the border between the two triangular cross-sections. From that point to the other end of assembly 10, the magnetostatic potential along boundary 24 decreases linearly to zero. Consequently, equipotential planes are defined in mantle 15 as indicated by solid lines 29. Adjacent magnet 13, the spacing of equipotential planes 29 intersecting boundary 24 is the same as that defined by equi-potential planes 21 inside the magnet Adjacent the cylindrical working space 14, the equi-potential planes along the cylinder wall define a uniform potential gradient and establish within space 14 a succession of fiat, parallel and uniformly spaced equi-potential planes 3%. Consequently, flux lines 20 extend through space 14 with uniform spacing, parallel to each other and parallel to axis 12, defining a homogeneous magnetic field within that space.

With this construction, there is zero radial flux entering or leaving space 14. Mantle 15 therefore produces no external flux. The condition that no flux may enter or leave boundary 24 is enforced by the magnitude and polarity of the magnetostatic potential along the boundary. While the potential changes linearly along boundary 24 in both the portion adjacent magnet 13 and the portion adjacent space 14, the change is normally at a greater rate adjacent the magnet.

It will be observed that space 14 is entirely surrounded by magnetic material. The outer end of space 14 is closed by shield 11. Because mantle 15 does not carry flux, no flux enters or leaves the conical portions of the shield. However, the shield serves to confine the return flux from magnet 13 into a path through the shield. Shield 11 preferably is of a high permeability material having negligible reluctance. It should be made of a material such as soft iron or one of the well-known high permeability alloys. In principle, the shield may be omitted in which case the return flux path is through the space outside the assembly, like with the ordinary unshielded solenoid. But the shield advantageously eliminates essentially all stray flux and, most significantly, the end portions of the shield, adjacent the magnet and the far end of the working space, serve to permit the flux to enter the shield directly and Without distortion in the space or in the magnet, thus insuring a uniform field of maximum length.

In theory, mantle 15 can be a single solid piece of material suitably magnetized to develop equi-potential planes 29. It is more convenient, however, to use separate sections 26 and 27 and to individually magnetize them prior to their assembly together. Additionally, fabrication and magnetization may be achieved more easily by constructing mantle or body 15 in the the form of a stack of washers having, from one end, successively increasing outer diameters up to plane 28 and from that plane to the other end having successively decreasing outer diameters. As illustrated, the spacing of equi-poten tial planes 29 (perpendicular to the planes) within section 26 is larger than within section 27; section 26, therefore, may be fabricated of a material bearing suitably smaller coercive force than section 27, or it may be suitably demagnetized before assembly.

As discussed above, a conventional sleeve-shaped permanent magnet includes added magnetic material to supply the unavoidable stray fiux which is in parallel to, and usually much larger than, the desired flux. In apparatus constructed in accordance with the present invention, however, the magnetic material which is added has different characteristics and is effectively in series with and is magnetized to oppose or buck out the stray flux in order to reduce the latter to zero; the mantle, therefore, constitutes of the core.

a magnetic insulator. In consequence, a much smaller structure is achieved. The assembly is superior to a solenoid because it requires no power .or cooling. Further, the complete assembly illustrated is entirely shielded and consequently produces no external stray fields.

Of course, care must be taken in adapting the principles of the invention to actual use. Compensation must usually be included for any departure from perfect symmetry as, for example, in providing apertures to accept electrical leads and the like feeding energy to internally disposed apparatus. However, such effects may be kept insignificant by minimizing the size of such apertures and, when that is not possible, by shaping the magnetizing field or the structure itself in order to compensate for any irregularities introduced.

With a material for mantle of given coercive force, and for a given flux density in the cylindrical working space 14, the thickness of the mantle is proportional to the axial length of the cylindrical space. Consequently, the volume of the mantle increases in an amount proportional to the square of the axial length; for small diameters of space 14, this increase is even larger. In order to reduce the volume of the mantle when a long drift space is required, the embodiment illustrated in FIGURE 4 may be employed. In essence, this form of the invention is composed of two halves each of which are constructed similarly to the assembly shown in FIGURE 2, but located so that one is the mirror image of the other. Shield 11a extends around the entire assembly of FIGURE 4 and is not disposed across the end of the FIGURE 2 portion which now defines the center plane 31 of the double assembly. The two halves of the assembly in FIGURE 4 are polarized in opposite directions, and center plane 31 becomes a plane of zero potential relative to the potential to either side. The flux within space 14a continues in a straight line across the center plane. Consequently, space 14a is of twice the length of space 14 in FIGURE 2, with an increase in material requirements by only a factor of two.

Throughout the above discussion, it has been assumed that magnet 13 is a permanent magnet. This is, of course, the most useful form of the invention because of the lack of any power or cooling requirements. Nevertheless, the principles involved contemplate constructing magnet 13 in the form of a winding on a core of magnetic material. The unique characteristics of mantle 15 are employed in such a combination to permit the development of a homogeneous, uniform magnetic field in the space off the end However, for the typical applications men tioned, the use of such an electromagnet is usually not preferred, because the ampere turns are approximately the same as in the ordinary shielded solenoid and its easier in the latter device to spread the turns in order to achieve the desired field shape.

As thus far discussed, assembly 10 has defined a cylindrical working space. However, the space can have any cross section and the nature and operation will be as described above as long as the space is completely surrounded by a mantle having the characteristics described above. If the cross section is quite wide in one dimension only, then the mantle along the small dimension can be omitted. Consequently, FIGURE 2 also represents an alternative construction in which space 14 is rectangular and of substantial width in the direction perpendicular to the plane of the drawing. If the width were infinite, a purely homogeneous field would be developed throughout space 14. But even with a practical width, as for example with a width approaching the height, the flux near the center of space 14 along axis 12 will be essentially homogeneous even though it may be severely distorted near the narrow sides of the space. Consequently, FIGURE 2 may be taken as depicting separate upper and lower body sections having symmetrical characteristics of the nature previously described.

Based upon the principles revealed above, the invention may be embodied in a number of different forms. One such alternative is illustrated in FIGURE 5 wherein upper and lower body portions 32 and 33, respectively, of magnetic assembly 34 form internal boundaries which define walls of a rectangular field space 35. Near one end of assembly 34, the inwardly-facing boundary surfaces of body portions 32, 33 taper outwardly and surround a magnet 36 of isoceles-trapezoidal cross-section. Enveloping the entire assembly is a shield 37. In this instance, assembly 34 has a width, in a direction perpendicular to the plane of the drawing, about ten times the height H of space 35.

The character and nature of the body portions, magnet, and shield, as well as the flux pattern developed in space 35, may be the same as that described above for the corresponding portions of assembly 10. Magnet 36 is magnetized in a direction to define a plurality of flat, parallel equi-potential planes uniformly spaced along and perpendicular to axis 12. Equi-potential planes developed in body portions 32, 33 intersect boundary 38 with :a spacing the same as that of the equi-potential planes inside magnet 36.

The desired magnetization of the magnet 36 preferably is achieved by utilizing a material such as oriented barium ferrite. A typical B-H curve for this material is depicted in FIGURE 6. It features a region of constant coercive force over a range of low flux densities. Magnet 36 is first fully magnetized and then assembled with the magnetized mantle 32, 33. As the magnets are joined, the central region of magnet 36 is de-magnetized to its correct operating flux density P (FIGURE 6); in the outer portions of magnet 36, the density decreases to zero (P in FIGURE 6) at its outer edge. However, since the coercive force remains constant, the equi-potential planes in the magnet remain parallel and evenly spaced.

The equi-potential planes in the body portions are symmetrical with respect to axis 12 and at their termini along space 35 serve to define in that space a plurality of equipotential planes that are fiat, parallel, and uniformly spaced along and perpendicular to axis 12. The magnetic flux produced in space 35 is generally homogeneous in a plane including axis 12 and parallel to the plane of the drawing. The return path for the flux is through shield 37.

As illustrated in FIGURE 5, space 35 is rectangular in a cross-section perpendicular to axis 12. Consequently, there will be flux distortion along the sides of space 35 unless it has an infinite width. As before, however, the flux is of substantial homogeneity in the immediate vicinity of axis 12. A perfectly symmetrical and uniform field may be achieved by modifying assembly 34 to have an overall frusto-conical shape; FIGURE 5 may then be interpreted as depicting a cross-section of such a structure. Also as described above, space 35 may have any desired cross section and yet have the desired flux pattern if the entire space is surrounded by a magnetic insulator of the kind described for the mantle.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A magnetic insulator comprising:

a hollow body of magnetic material having a longitudinal cross-section of generally triangular shape in a given plane and magnetized in a direction, in said plane, perpendicular to an outer side of the triangle to produce a magnetostatic potential which increases generally linearly along an internal boundary thereof.

2. A magnetic insulator comprising:

a body of magnetic material having a cross-sectional shape in a given plane composed of a pair of generally triangular sections with bordering respective first sides and aligned respective second sides together defining a boundary, each of said sections being magnetized in a direction, in said plane, perpendicular to its third side to produce a magnetostatic potential which changes substantially linearly along said boundary as measured along a line lying in said plane, said potential increasing along the boundary from one end of said body to the border formed by said first sides and decreasing from said border to the other end of said body.

3. A magnetic assembly comprising:

a body of magnetic material exhibiting substantially zero flux density, said body being magnetized in a predetermined direction in a given plane to produce a magnetostatic potential, as measured along a line lying in said plane, increasing substantially linearly along one boundary thereof from one end of said body to an intermediate region and decreasing substantially linearly from said region to the other end of said body;

and a magnet disposed along a portion of said boundary between said one end and said region with said magnet being polarized to develop generally parallel flux lines and with generally flat, uniformly spaced and parallel equi-potential planes spaced successively along and generally perpendicular to an axis parallel to the portion of said boundary between said region and said other end, said equi-potential planes defining a change of potential corresponding to that in said body along the boundary portion adjacent the magnet.

4. A magnetic assembly as defined in claim 3 in which said body, including said magnet, is substantially entirely enclosed within a confroming shield of high permeability material having substantially low magnetic reluctance.

5. A magnetic assembly as defined in claim 3 in which said body is composed of a plurality of stacked segments individually magnetized to develop said magnetostatic potential.

6. A magnetic assembly comprising:

a hollow body having a longitudinal cross-section of generally triangular shape in a given plane and exhibiting substantially zero flux density, said body being magnetized in a predetermined direction in sa d plane to produce a magnetostatic potential increasing substantially linearly along one boundary thereof from one end of said body to a plane transverse to said given plane and decreasing substantially linearly from said transverse plane to the other end of said body;

and a magnet disposed along a portion of said boundary between said one end and said plane with said magnet being polarized to develop flux lines generally parallel to said boundary and with generally fiat, uniformly spaced and parallel equi-potential planes spaced successively along and generally perpendicular to said boundary portion, said equi-potential planes defining a change of potential corresponding to that in said body along said portion.

7. A magnetic assembly comprising:

at least two body sections each defining a boundary, each body section magnetized in a predetermined direction in a given plane to produce a magnetostatic potential increasing, as measured along a line lying in said plane, along a first portion of said boundary from one end of the body to an intermediate plane transverse to said given plane and decreasing from said transverse plane along a second boundary portion to the other end of said body and said boundaries defining a space therebetween;

and a magnet disposed in said space adjacent said first boundary portion with said magnet being polarized to develop generally parallel flux lines and having generally flat and parallel equi-potential planes uniformly spaced along and perpendicular to an axis parallel to said second boundary portion with said equi-potential planes defining a potential gradient in said magnet substantially coinciding with the change of potential along said first boundary portion adjacent the magnet, the potential gradient along said second boundary portion resulting in generally fiat, parallel equi-potential planes uniformly spaced in the adjacent part of said space from said plane substantially to said other end.

8. A magnetic assembly as defined in claim 7 in which said body, including said magnet and said space, is substantially entirely enclosed within a conforming shield of high permeability material having substantially low a magnetic reluctance.

9. A magnetic assembly comprising:

a hollow, generally cylindrical body composed of a pair of annular generally frusto-conical sections having a common base and together defining the boundary of an interior space, each of said sections being magnetized in a direction perpendicular to its outer wall to produce a magnetostatic potential increasing along a first portion of said boundary from one end of the body to said base and decreasing from said base along a second boundary portion to the other end of the body;

and a magnet disposed in said space adjacent said first boundary portion with said magnet being polarized to develop flux lines generally parallel to said boundary and having generally fiat and parallel equi-potential planes uniformly spaced in a direction parallel to and perpendicular to the boundary with said equipotential planes defining a potential gradient in said magnet substantially coinciding with the change of potential along said first boundary portion adjacent the magnet, the potential gradient along said second boundary portion resulting in generally flat, parallel equi-potential planes uniformly spaced in the adjacent part of said space from said base substantially to said other end.

10. A magnetic assembly comprising:

a magnet polarized in a predetermined direction in a given plane to develop within its interior flux lines disposed generally parallel to a predetermined axis in said plane;

and flux-opposing means edefining a space on said axis adjacent one surface of said magnet of one polarity and including a permanent magnet material disposed in series with a normal stray flux path from said space to the oppositely polarized surface of said magnet and having a magnetization potential and polarity of magnitude and of direction in said plane, respectively, to establish minimum flux density in said stray flux path, said assembly defining a return flux path around said flux-opposing means from the end of said space remote from said one surface to said other surface.

11. A magnetic assembly as defined in claim 10 in which the coercive force in said magnet is of a value to develop equi-potential planes in said magnet having a spacing corresponding to that of the equi-potential planes in said material adjacent the magnet.

12. A magnetic assembly comprising:

a magnet polarized in a predetermined direction in a given plane to develop within its interior flux lines disposed generally parallel to a predetermined axis in said plane;

flux-opposing means defining a space on said axis adjacent one surface of said magnet of one polarity and including a permanent magnet material disposed in series with a normal stray flux path from said space to the oppositely polarized surface of said magnet and having a magnetization potential and polarity of magnitude and direction in said plane, respectively,

to establish minimum fiux density in said stray flux path;

and a high-permeability shield across at least the end of said space remote from said one surface and constituting at least a portion of a return flux path from said end to said other surface.

13. A magnetic assembly comprising:

a magnet magnetized in a predetermined direction in a given plane to define a plurality of equi-potential planes generally fiat, parallel, uniformly spaced and perpendicular to an axis in said plane and along which the magnet is disposed;

and a body of magnetic material disposed along said axis, eifectively having a common boundary with the sides of said magnet, and defining a space on said axis, said body having magnetostatic equi-potential planes establishing a gradient, as measured along a line lying in said plane, along said boundary corresponding to that defined by the equi-potential planes in said magnet and defining in said space a plurality of flat, parallel equi-potential planes uniformly spaced along and perpendicular to said axis.

14. A magnetic assembly as defined in claim 13 in which said magnet is of a material exhibiting a flux density region having constant coercive force, with said magnet having a flux density in said region of given strength in the vicinity of said axis and of lesser strength outwardly therefrom.

15. A magnetic assembly as defined in claim 13 in which said space is entirely enveloped by a material exhibiting the characteristics defined for said body.

16. A magnetic assembly as defined in claim 13 in which a second magnet like the first and a second body like the first are disposed along said axis to define essentially a mirror image, of the first body and magnet, about a center plane, with said first and second bodies abutting at said center plane.

17. A magnetic assembly comprising:

a magnet of isosceles-trapezoidal cross-section magnetized to define a plurality of equi-potential planes generally flat, parallel, uniformly spaced and perpendicular to the axis of the magnet;

and at least two body sections of magnetic material symmetrically disposed on opposite sides of said axis, having a common boundary with the side of said magnet and with said sections defining a space therebetween on said axis, said sections having magnetostatic equi-potential planes establishing a gradient along said boundary corresponding to that defined by the equi-potential planes in said magnet and defining in said space a plurality of flat, parallel equiit) potential planes uniformly spaced along and perpendicular to said axis.

18. A magnetic assembly comprising:

a body of magnetic material exhibiting substantially zero flux density, said body being magnetized in a predetermined direction in a given plane to produce a magnetostatic potential, as measured along a line lying in said plane, increasing in accordance with a selected gradient along a selected portion of one boundary thereof;

and a magnet disposed along a different portion of said boundary with said magnet being polarized to develop flux lines creating equi-potential planes outside said body and spaced successively along said selected portion of said boundary, said equi-potential planes defining a change of potential along said selected portion corresponding to that of said selected gradient in said body.

19. A magnetic assembly as defined in claim 18 in which said body, including said magnet, is substantially entirely enclosed Within a conforming shield of high permeability material having substantially low magnetic reluctance.

20. A magnetic assembly comprising:

a body of magnetic material exhibiting substantially zero flux density, said body being magnetized in a predetermined direction in a given plane to produce a magnetostatic potential, as measured along a line lying in said plane, increasing in accordance with a selected gradient along one boundary thereof from one end of said body to an intermediate region and decreasing in accordance with a predetermined gradient from said region to the other end of said body;

and a magnet disposed along a portion of said boundary between said one end and said region with said magnet being polarized to develop flux lines creating equi-potential planes spaced successively along said boundary, said equi-potential planes defining a change of potential along said boundary corresponding to that of said gradients.

References Cited by the Examiner UNITED STATES PATENTS 2,817,038 12/ 1957 Hickey.

3,079,535 2/1963 Schultz 317201 FOREIGN PATENTS 307,469 8/ 1955 Switzerland.

JOHN F. BURNS, Primary Examiner.

LARAMIE E. ASKIN, E. JAMES SAX, Examiners.

Disclaimer 3,227,931 R0bert Adler, Northfield, Ill. PERMANENT-MAGNET UNI- FORM-FIELD-PRODUCING APPARATUS. Patent dated J an. 4,

1966. Disclaimer filed J an. 12, 1970, by the assignee, Zenith Radio Corporation.

Hereby enters this disclaimer patent.

to claims 1, 10, 11, 13, 14 and 15 of said [Oflicz'al Gazette A m'il 14, 1.970.] 

1. A MAGNETIC INSULATOR COMPRISING: A HOLLOW BODY OF MAGNETIC MATERIAL HAVING LONGITUDINAL CROSS-SECTION OF GENERALLY TRIANGULAR SHAPE IN A GIVEN PLANE AND MAGNETIZED IN A DIRECTION, IN SAID PLANE, PERPENDICULAR TO AN OUTER SIDE OF THE TRIANGLE TO PRODUCE A MAGNETOSTATIC POTENTIAL WHICH INCREASES GENERALLY LINEARLY ALONG AN INTERNAL BOUNDARY THEREOF. 